Tickle a rat and it will jump for joy, gleefully squeak and beg for more. In addition to describing these delightful reactions to a tickling hand, a new study identifies nerve cells in the brain that help turn rats into squirmy puddles of giggles.

The results, published November 11 in Science, offer insight into how the brain creates glee, an understudied emotion. “People really underrate the positive things — fun, happiness, joy,” says study coauthor Shimpei Ishiyama of Humboldt University of Berlin.

Scientists knew that rats seemed to enjoy a good tickle from a human, but how the brain creates that emotion was a mystery. Although no protocol existed, the tickling part of the experiment turned out to be “surprisingly easy,” Ishiyama says. He simply stuck his hand in the cages and scribbled his fingers in the rats’ fur, to

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